Vapor lamp for sound recording



Aug. 10, 1943. A G, FOOTE VAPOR LAMP FOR scum) RECORDING Filed Nov. 2, 1940 lnven+orc- UJ. o. o m. rm G LT n A m m M Patented Aug. 10, 1943 VAPOR, LAMP FOR SOUND RECORDING Alton G. Foote, Wicklifie, Ohio, assignor to General Electric Company, a corporation of New York Application November 2,1940, Serial No. 364,019

. 4 Claims; (Cl. 176-122) My invention relates to gaseous discharge devices of the metal vapor type and more particularly to mercury vapor lamps for the production of the ultra-violet light used in the recording of sound waves on films.

The use of ultra-violet light for the recording of .sound wave patterns on photographic films has become increasingly prevalent primarily for the reason that films are more photosensitive to the shorter wave lengths of light. In the past it has been the practice to employ high temperature incandescent filaments as a source of the ultra-violet radiation although the practice has been subject to the disadvantage that the high temperature considerably shortens the lamp life. Although mercury vapor lamps are, as is well known, rich in ultra-violet, they have not hitherto been altogether satisfactory primarily because the condensed vapor falling back to the pool through the arc space (the so-called fmercury rain phenomenon) as well as the condensed liquid mercury on the tube walls themselves have interfered with the light output. Now I have found that this defect can be largely avoided by so shaping the bulb that the excess mercury vapor will flow away from the are space in such a direction that it condenses at a portion of the tube wall remote from the outlet for the useful light. By this expedient the used portion of the tube wall is kept clear of condensed mercury and the space between the arc and that portion is kept relatively free of falling mercury drops.

It is therefor one of the objects of my invention to construct a mercury vapor lamp which will be free of the aforementioned objections.

Another object of my invention is to construct a mercury vapor tube the operation of whichis relatively unaffected by transportation and by envelope 2 of glass or quartz, an anode 3, pref-- erably of tungsten, and cathode 4. The envelope 2 may be considered as being divided into an tion shown also contains the stem I2, and a bulb portion 6 surrounding the anode and cathode. The anode 2 terminates in the head I which is positioned directly below the cathode and which makes it possible to handle higher currents with a given size shank. The loop 8 increases the effective length of the anode lead in order to give cooler operation of the neck portion. As will be seen presently, it is desirable to operate this Theportion at a relatively low temperature. cathode 4 incorporates an activated portion [0 formed by winding three layers of fine tungsten wire, each successive layer in the opposite direction, on a larger size tungsten wire and then coiling the whole. The portion It! may be dipped in molten barium hydroxide or otherwise suitably coated before sealing in and treatment on the exhaust. The three layers of fine wire make it possible to carry sufiicient active material to give a reasonable life at currents normally considered high for cathodes of such dimensions. The shield 9 covering the portion l0 aids in keeping the bulb clean. For supplying an ionizable working vapor to the tube, the mercury pool H is added. Its close proximity to the anode 3 promotes the ready vaporization of the mercury by heat from the anode.

The tube shown is designed primarily for direct current battery operation although it may also be used with an alternating current power source. I have found that the arc will strike with a voltage difierence of about 8 volts between electrodes. When normal operating temperature and pressure have obtained the' arc voltage is about 13 volts.

Normally the tube will operate -in the horizontal position shown. In this position, the mercury will be sufiiciently close to the anode to absorb sufficient heat therefrom to .vaporize readily. Further, with the envelope configuration shown, the tubemay be rotated approximately 10" in any direction without appreciably increasing the distance between the anode and mercury pool. Because the arc is separated from the neck portion bya considerable distance and because "of the horizontal operation, the neck portion will run at a considerably lower temperature'than the region of the arc. The result will be that the mercury vapor rising from the pool and passingaround the arc will condense in'theneck portion and run back to the pool along the bottom of the bulb. The portion "of the bulb surface between the arc and the optical,

system is thus kept clear of condensed mercury extended neck portion 5, which in themodificaand the space between the arc and this same bulb portion is relatively free of condensed 'mercury falling back to the pool.

It will be understood that the tube herein disclosed is illustrative of but one embodiment of my invention, and that many modifications within the scope of the appended claims may occur to those skilled in the art to which the invention appertains. For example, a wide range of bulb configurations permitting the mercury to condense away from the light emitting portions may be possible. Thus the neck portion in which the mercury condenses need not necessarily coincide with the portion containing the stem l2, as shown in the drawing, but may be any extended chamber attached to a suitable portion of the bulb. All such modifications I longitudinally therethrough to the vicinity ofthe bulb end of the envelope, a pair of electrodes carried by said conductors in the bulb end of said envelope, one of said electrodes being located adjacent to the axis of the envelope and the other electrode being located below said axis so that the discharge gap therebetween extends transversely of said axis, a downwardly concave shield mounted adjacent to and above the upper electrode, and a pool of mercury disposed in said envelope below said electrodes, the stem end portion of said envelope serving to condense the mercury vaporized during operation of the lamp. 7

2. A mercury vapor lamp comprising a sealed envelope adapted for use with its longitudinal axis disposed horizontally and having a stem end and a bulb end, a pair of lead-in conductors sealed in the stem end of said envelope and extending longitudinally therethrough ,to the vicinity of the bulb end of the envelope, a filamentary electrode mounted across said conductors at the bulb end of the envelope and adjacent the axis thereof, a downwardly concave shield mounted on one of said pair of lead-in conductors adjacent to and above said 'filamentary electrode, a third lead-in conductor conductor below said filamentary electrode so that the discharge gap between said electrodes extends transversely of said axis, and a pool of mercury disposed in said envelope below said electrodes, the stem end portion of said envelope serving to condense the mercury vaporized during operation of the lamp;

3. A mercury vapor lamp comprising a sealed envelope adapted for use with its longitudinal axis disposed horizontally and having a stem end and a bulb end, a filamentary electrode at the bulb end of said envelope and adjacent its longitudinal axis, a downwardly concave shield mounted adjacent to and above said filamentary electrode, a second electrode mounted below said filamentary electrode so that the discharge gap therebetween extends transversely of said envelope axis, and a pool of mercury disposed below said electrodes in close-proximity to the lower electrode, the stem end portion of said envelope extending a substantial distance from said electrodes and servingto condense the mercury vaporized during operation of the lamp.

4. A mercury vapor lamp comprising a sealed envelope adapted for use with its longitudinal axis disposed horizontally and having a stem end and a bulb end, a pair of lead-in conductors sealed in the stem end of said envelope and extending longitudinally therethrough to the vicinity of the bulb end of the envelope, a filamentary electrode mounted across said conductors at the bulb end of the envelope and adjacent the axis thereof, a third lead-in conductor sealed in the stem end of said envelope and extending longitudinally and downwardly therethrough, a second electrode carried by said third conductor below said filamentary electrode so that the discharge gap between said electrodes extends transversely of said axis, said third conductor being distorted intermediate its ends to increase its effective length and thereby minimize dissipation of heat from said second electrode to the stem end of the envelope, and a pool of mercury disposed in said envelope below said electrodes, the stem end portion of said envelope serving to condense the mercury vaporized during operation of the lamp.

ALTON G. FOO'I'E. 

